BIOACCUMULATION OF ENVIRONMENTAL CONTAMINANTS IN OYSTER (Crassostea sp.) TISSUES IN BAYELSA STATE, NIGERIA

Abstract

This study assessed the levels of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in oyster (Crassostrea sp.) tissues collected from the St. Nicholas River in Brass Local Government Area, an oil-impacted mangrove ecosystem in Nigeria. Heavy metal analysis revealed that of the three metals tested—cadmium (Cd), mercury (Hg), and zinc (Zn)—only zinc was detected. Zinc concentration was significantly higher in dried oyster samples (0.350 µg/g) compared to fresh samples (0.110 µg/g), but remained within the WHO/FAO permissible limit of 3 µg/g. Cadmium and mercury were not detected in either sample type. PAH analysis identified thirteen congeners in the oyster tissues. In dried oysters, fluorene (56.06 ± 0.10 µg/g dry weight) and benzo(a)pyrene (9.36 ± 0.01 µg/g) were the most abundant, while naphthalene had the lowest concentration (0.08 ± 0.10 µg/g). In fresh oysters, benzo(a)pyrene was highest (1.47 ± 0.20 µg/g), and phenanthrene was lowest (0.03 ± 0.20 µg/g). Over 80% of detected PAHs exceeded WHO/FAO permissible limits, including acenaphthylene (1.16 ± 0.16 µg/g vs. limit of 0.01 µg/g), fluorene (56.06 µg/g vs. 0.001 µg/g), and benzo(k)fluoranthene (7.51 ± 0.27 µg/g vs. 0.1 µg/g). Statistical analysis using the Student’s t-test revealed significant differences in contaminant concentrations between dried and fresh oysters (p < 0.05), confirming bioaccumulation. The findings implicate crude oil pollution, unregulated waste disposal, and combustion byproducts as primary sources of contamination. This study concludes that Crassostrea sp. is a reliable sentinel species for environmental monitoring and highlights the urgent need for pollution control, routine monitoring, and community sensitisation to mitigate public health risks